Research Update: Jumping Worms and Sleeping Cocoons

The invasive

The invasive "jumping worm" (genus Amynthas).

The embrace of warm spring weather has many people asking about the “jumping worms” (Amynthas species) that were found inhabiting the Arboretum in fall 2013.

All earthworms found in Wisconsin are non-native. They arrived during European settlement of the Great Lakes region. Most of these earthworms are from the same family (Lumbricidae). Earthworms are classified into three ecological groups according to their feeding and burrowing behavior. In general, earthworms consume leaf litter and organic materials, release nutrients, and alter soil structure.

Adult Amynthas agrestis (left) and Amynthas tokioensis (right). (Photo: Marie Johnston)

In 2013, earthworms of a new family (Megascolecidae) were confirmed in Wisconsin. Two species of jumping worm were found in the forests of the Arboretum—the larger Amynthas agrestis and the smaller Amynthas tokioensis. They earned their common name due to rapid side-to-side motion and lively behavior upon being handled. They are competitive with other species, grow rapidly, and transform an intact soil surface into loose casts. In the forest or garden landscape, these earthworms may pose a threat to plant establishment, root growth, and nutrient uptake.

The jumping worms are different from other earthworms found in Wisconsin because they (1) originate from East Asia, not Europe; (2) inhabit the soil surface directly below the leaf litter layer, rather than dwelling in deeper soil layers; (3) are parthenogenic, which means they can self-fertilize; and (4) have an annual life cycle and mature at the same time near the end of summer. Each new generation begins with the production of hardened egg capsules, known as cocoons, that overwinter in the soil to hatch the following spring.

Amynthas cocoon (at arrow) surrounded by earthworm casts. (Photo: Marie Johnston)

For land managers, these differences in habitat and life cycle make controlling the earthworms a challenge. First, it can be difficult to identify jumping worms until a few months into the growing season because the young worms are small (1–3 cm long when they hatch from the cocoon). Second, the cocoons are inconspicuous and a similar size (1–3 mm diameter) and color of soil aggregates. Third, jumping worms have a flexible diet and are suited to surviving in less-opportune environments, such as below hardwood mulch. Their unnoticed presence in plant, soil, and bark products, combined with the cocoons’ resilience to cold and drought, may help explain how jumping worms spread across urban areas.

Research is underway at the Arboretum to determine environmental limitations of the “sleeping” Amynthas cocoons—that is, while they are inactive over the winter months—so that we might improve management practices to slow the spread of jumping worms.

Cocoons of Amynthas agrestis (left) and Amynthas tokioensis (right). (Photo: Marie Johnston)

Last fall, a laboratory study was set up to acquire Amynthas cocoons of known species and age. Adult Amynthas earthworms of each species were collected and housed in plastic tubs containing soil that was pre-ground to a small aggregate size (smaller than the cocoons). Then, after 20 days, any cocoons produced were removed, counted, and stored in glass vials at room temperature for later study.

Since a key factor to the jumping worms’ success in Wisconsin is that the cocoons can overwinter in soil, temperature trials were set up to test cocoon viability upon exposure to cold and heat. In one finding, the heat tests suggest jumping worm cocoons do not survive the temperatures reached in commercial composting—this is potentially good news because even as the research results are in progress, it is likely that licensed compost products (treated according to state law) are probably free of jumping worms.

Young Amynthas tokioensis (top) and another earthworm that lives in the litter layer (Eisensia fetida, bottom). (Photo: Marie Johnston)

Hatchlings in the laboratory confirm that jumping worm babies look just like the adults, except that they lack the easily identifiable light-colored clitellum seen on mature Amynthas worms. The hatchlings look like other small earthworms you might find in similar habitats. The best way to confirm their identity is to use a microscope.

Research on jumping worm cocoons has helped affirm the benefit of several best management practices for controlling the spread of earthworms. For example, although the cocoons are small, cleaning soil from equipment, plant roots, and deep treads should also remove the cocoons. Future research will address the treatment of leaf, mulch, and soil products to minimize cocoon viability and accidental transport of worms and cocoons in these materials. Arboretum research plans also include monitoring the spread of these earthworms throughout the state and developing methods to clear invaded materials of worms and cocoons.

Property owners who suspect they have jumping worms should keep any potentially invaded plant, soil, and mulch on their site—these materials should not be shared with anyone or transplanted on other properties. Sightings of jumping worms should be reported to the Wisconsin DNR by emailing the agency or uploading a photo to the First Detector’s Network.

—Marie Johnston, postdoc, UW–Madison Department of Soil Science and Arboretum

To learn more about the jumping worms, see the Arboretum’s Amynthas information sheet (PDF).